1. Field of the Invention
This invention relates to a method and an apparatus for sensing a magnetic field and for detecting a magnetic flux density, each as a function of a measured Lorentz force.
2. Discussion of Related Art
Hall sensors have been used to sense magnetic fields. Hall effect transducers have been used with pole pieces and biasing magnets to increase sensitivity of the Hall sensors. When used with a magnet, a pole piece tends to channel a magnetic field and thus change flux densities in a magnetic circuit.
U.S. Pat. No. 4,992,659discloses a microscopy apparatus for measuring Lorentz force-induced deflection of a tip of a scanning tunneling microscope to image magnetic structures of a sample. Motion of the tip, which indicates the presence of a magnetic field, is optically detected. The magnetic field measurement and a tip position are received by a computer which provides an output signal to a device for graphically representing the magnetic field at different positions on a surface of the sample.
U.S. Pat. No. 5,675,252discloses a piezomagnetometer which uses a magnetoelectric composite structure, formed by alternating layers of piezoelectric and magnetostrictive material, to convert a fluctuating magnetic field directly to electric current. An ambient magnetic field strains magnetostrictive layers which stresses piezoelectric layers and drives a polarization current proportional to an amplitude of the magnetic field.
It is apparent that there is a need for a method and apparatus that enables a microelectronic structure to sense a magnetic field and to measure a magnetic flux density. There is also a need for a method and apparatus that produces a significantly higher output voltage, as compared to conventional methods and apparatuses, when exposed to the same magnetic field.
It is one object of this invention to provide a method and apparatus that uses a Lorentz force and a piezoelectric effect to detect the presence of a magnetic field and to measure a magnetic flux density of the magnetic field.
It is another object of this invention to provide a microelectronic structure that detects the presence of a magnetic field and measures a magnetic flux density of the magnetic field.
It is still another object of this invention to provide a method and apparatus that produces a significantly higher output voltage signal, as compared to known methods and apparatuses, when exposed to the same magnetic field.
The above and other objects of this invention are accomplished with a method for sensing a magnetic field wherein a direct-current voltage is applied across a first layer of a conductive material. A direct current flows in a first direction through the first layer. A second layer of piezoelectric material is either integrated with or is adhered to the first layer. The first layer and the second layer are positioned within or exposed to the magnetic field. A Lorentz force generated in a second direction, which is preferably but not necessarily generally perpendicular to the first direction, is generated causing the piezoelectric material to deflect. The presence of a magnetic field and/or a magnetic flux density of the magnetic field can be calculated as a function of the measured Lorentz force.
In one preferred embodiment according to this invention, the direct current is in a range of about 0.1 mA to about 10 mA, and preferably about 3 mA. Also in a preferred embodiment of this invention, a magnitude of the magnetic flux density is in a range of about 100 Gauss to about 1,000 Gauss, preferably about 400 Gauss.
The first layer of the conductive material and the second layer of the piezoelectric material can be moved within the magnetic field into a position where the magnitude of the Lorentz force is at a maximum value. In such position where the Lorentz force is at a maximum value, the two vectors representing the direct current and the magnetic field are at a right angle with respect to each other. The Lorentz force is generated in a direction which is preferably generally perpendicular to the directions of the vectors of the direct current and the magnetic field.
In one preferred embodiment according to this invention, an apparatus for sensing a magnetic field comprises the first layer of the conductive material integrated with, or applied to, the second layer of the piezoelectric material, such as by a sputtering technique or other suitable deposition technique. As the layer of piezoelectric material changes shape it produces a change in voltage. A sensor can then measure the Lorentz force generated by measuring the voltage. A computer is preferably used to receive the transducer output signal corresponding to the measured Lorentz force. The computer then calculates either the presence of a magnetic field or a magnitude of the magnetic flux density, as a function of the measured Lorentz force, using any suitable analog and/or digital circuit.